Method and compositions for producing condensable combustion products



United States Patent METHOD AND COMPOSITIONS FOR PRODUCING CONDENSABLE COMBUSTION PRODUCTS Leonard Greiner, Palo Alto, Calif., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware No Drawing. Filed July 18, 1966, Ser. No. 565,697

10 Claims. (Cl. 60207) ABSTRACT OF THE DISCLOSURE A method for generating condensable combustion products at non-stoichiometric O/F for use in an underwater power plant which comprises reacting a non-nitrogenous oxidizer with a non-nitrogenous fuel and reacting the gaseous reaction products with sulphur or a non-nitrogenous sulphur compound.

Background of the invention This invention relates to underwater propulsion systems and more particularly to a method and compositions for operating underwater combustion systems such that the gaseous combustion products produced are substantially free of non-condensable products.

As used herein, the term condensable" refers to originally gaseous combustion products that either are rapidly soluble in water or react physically or chemically with water to form solids, liquids or water soluble gases. For practical reasons and, as used herein, a gaseous combustion product is considered to be condensable if it contains substantially less than 1%, and preferably less than .5 by volume of permanent gases.

In underwater propulsion systems, it is desirable to produce condensable exhaust gases for several reasons. The first and most obvious is that it is desirable to eliminate a wake of gas bubbles which makes visual and sonar detection of underwater devices much easier.

Another and perhaps more important reason is that condensuctors will not function properly if permanent gases such as 0 H N and C0 are present in the exhaust products in amounts greater than about 1% by volume. CO although not very soluble can be tolerated in small amounts, up to 5% by volume, in the gas stream. Condensuctors are described in Astronautics and Aeronautics, March 1965, pp. 50-54, and many underwater propulsion systems which operate at substantial depths employ such devices. The condensuctor mixes the exhaust gases with ambient sea water and in effect provides a back pressure to the turbine, reaction or reciprocating motor that is fairly constant regardless of depth; this back pressure being approximately of the order of magnitude of the vapor pressure of water at the temperature in the condensuctor which is considerably below normal ambient pressures of depth. If non-condensable gases are present, the condensuctor functions inefiiciently and the engine senses a back pressure that approaches or equals the hydrostatic head at the level of operation. Since pressure in p.s.i. is approximately equal numerically to /2 the depth in feet, operation at a depth of about 500 feet would produce a back pressure of about 250 p.s.i. substantially reducing both the pressure drop across the prime mover and the efiiciency of the prime mover. It is possible to r 4 3,404,531 Ice Patented Oct. 8, 1968 deviation from which causes non-condensable gases to form. In practice, it is difficult to maintain this precise ratio under the conditions encountered, and it becomes especially difiicult if any thrust modulation of the system is utilized. Accordingly, even such properly designed systems tend to produce the undesirable non-condensable gases.

According to this invention, it has been found that condensable gaseous combustion products can be produced from reaction of conventional non-nitrogenous fuels and oxidizers across a wide spectrum of O/F ratios if sulphur or a non-nitrogenous sulphur-containing compound is available for reaction with the combustion products. Sulphur, either in elemental form or in a compound, has the unique ability of reacting in either fuel or oxidizer-rich environments to produce condensable products, thereby eliminating the necessity of operating underwater propulsion devices at a specific 0/ F ratio.

Accordingly, it is an object of this invention to provide a method of operating an underwater propulsion device to produce condensable gaseous combustion products.

It is another object of this invention to provide a reaction system for underwater propulsion devices that produces condensable gaseous reaction products at varying 0/ F ratios.

It is a further object of this invention to provide a source of sulphur in addition to the primary fuel and oxidizer of an underwater propulsion system.

These and other objects of this invention will be readily apparent from the following description of this invention.

Description of the invention According to this invention, sulphur, either in elemental form or in the form of a non-nitrogenous compound, is used in conjunction with conventional non-nitrogenous fuels and oxidizers employed in liquid, slurry or hybrid fueled underwater propulsion devices to produce combustion products, the gaseous components of which are only condensable gases regardless of whether the propulsion device is operated at stoichiometric fuel-rich or oxidizer-rich O/F ratios.

Generally, the non-condensable products produced at fuel-rich O/F ratios will be hydrogen and carbon monoxide and, at oxidizer-rich ratios, will be oxygen. Sulphur reacts to produce water soluble products in both conditions as follows:

Fuel rich Oxidizer rich Thus, if the propellant system is substantially free of nitrogen and is limited in carbon content such that the gaseous working fluid contains less than 5% by volume of CO sulphur or sulphur-containing compounds can be employed to produce combustion gases which are substantially free of non-condensable gases. The propellant system is considered to be substantially free of nitrogen if the gaseous exhaust from the system contains less than 1% by volume nitrogen. It is not possible to set'forth limits to the amount of sulphur that must be present since this value will vary with characteristics of each particular system. The amount of sulphur needed in each individual case can be readily determined by a worker in the art by estimating the maximum permissible variance from a stoichiometric O/F ratio that can be tolerated in a particular system, and then providing sufiicient sulphur to react with all the non-condensable gases produced under these most unfavorable conditions.

The fuels usable in this invention include but are not limited to metals such as the alkali metals, beryllium, boron, zirconium, aluminum, magnesium and metal hydrides, carbides, and borides. Hydrocarbon fuels such as diesel fuel or non-nitrogenous polymeric binders may be used with the above fuel materials if the amounts used are kept sufiiciently low to produce no more than CO by volume in the combustion gases. The fuel material may be utilized in solid form, as slurries in a fluid carrier, or in flowable or molten condition.

Suitable non-nitrogenous oxidizers include oxygen, water, hydrogen peroxide, water-soluble halogens and compounds of such halogens, and various non-nitrogenous oxidizing acids and salts and metallic peroxides such as alkali metal chlorates, perchloric acid, alkali metal perchlorates, and alkali metal peroxides.

The sulphur-containing material may be physically ad mixed with the fuel or oxidizer material or may be included in or added independently to the combustion chamber or may be reacted with the combustion products at a point downstream of the combustion chamber.

The sulphur is preferably supplied in the form of ele mental sulphur, however, non-nitrogenous organic and inorganic sulphur compounds can also be employed as a source of reactive sulphur. Suitable compounds include, but are not limited to, hydrogen sulfide, metallic sulfides and sulphates, carbon disulfide, dimethyl sulphoxide, dimethyl disulfide, mercaptans and sulphur-containing polymers such as Thiokol polysulfide rubberf When organic compounds are employed, it is necessary to limit the total amount of carbon present in both the fuel and the sulphur source so that CO can be maintained at less than 5% of the exhaust gases. Accordingly, it is usually desirable to include additional amounts of sulphur in addition to the sulphur-containing compound.

When sulphur compounds are admixed with the fuel to provide a source of sulphur, instead of elemental sulphur, the non-sulfuric elements of the compound must be considered as either fuel or oxidizer components in determining the stoichiometry of the system.

Thus, if a compound such as carbon disulfide is used, one atom of carbon must be considered as fuel in the stoichiometric balance for every two atoms of sulphur present. Likewise, if dimethyl disulfide is employed, one atom of carbon and three atoms of hydrogen must be considered as fuel for each atom of sulphur present.

A more complex situation exists where a compound contains both fuel and oxidizer elements as is the case with dimethyl sulfoxide. In determining overall stoichiometry, two atoms of carbon and six atoms of hydrogen must be treated as fuel and one atom of oxygen as oxidizer for each atom of sulphur present.

EXAMPLE 1 A fuel mixture having the following composition is thoroughly mixed and compressed into a hybrid fuel grain:

Component: Percent by weight Thiokol (polysulfide binder) Sulphur powder Magnesium powder 75 The grain is combusted with liquid perchloric acid dihydrate (HClO -2H O) in a hybrid combustion chamber and sea water is added to the combustion products in the combustion chamber to lower the temperature of the products to about 1800 R, which is suitable for use in a heat engine. The combustion chamber pressure is 1000 p.s.i.a. and the gases are expanded to 50 p.s.i.a. in the heat engine, at which point they contact the seawater in the condensuctor.

At a stoichiometric O/F ratio, 17.2 g. of the fuel will react with 22.8 g. of the oxidizer. When the combustion products are mixed with about 60.0 g. of water, a temperature of about 1885 F. is produced in the combustion chamber and the working fluid will have approximately the following composition at the condensuctor:

Component: Moles MgO .5 31 CO .052 HCl .167 H O 3.650 H .002 so .034 H 8 .066 S (g) .001

As can be seen, the only non-condensable gas present is hydrogen which is present in less than .05 of the total gases present and well within tolerable limits. If thereactants are off stoichiometric O/F ratio by having 10% excess fuel, the working fluid will have approximately the following composition at the condensuctor:

Component: Moles MgO .565 C0 .055 HO] 1.590 H O 3.610 H S .094 H .003 S0 .013

Again, hydrogen is the only non-condensable gas present; this time at less than 0.08% and also within tolerable limits. If the reactants are off stoichiometric O/F ratio by having 10% excess oxidizer, the working fluid will have the following approximate composition at the condensuctor:

Component: Moles MgO .503 C0 .049 HCl .174 H O 3.680 S0 .053 H 8 .042 H .001

Virtually no non-condensable gases are present in the working fluid. In the absence of sulphur, the fuel-rich system would produce about 1.75% of hydrogen and the oxidizer-rich system would produce about .8% oxygen.

EXAMPLE 2 An aluminum fuel is combusted with gaseous oxygen and the combustion products mixed with water as described above. A stoichiometric reaction with aluminum proceeds according to the following formula:

and requires 53 parts by weight of aluminum and 47 parts by weight of oxygen. In the event that the O/F ratio is off stoichiometric by being 10% fuel-rich, the excess aluminum will react with water to produce non-condensable hydrogen. Likewise, if the O/F ratio is off stoichiometric by being 10% oxidizer-rich, the excess oxygen remains as a non-condensable gas in the combustion products. However, if the fuel is formulated to consist of by weight Al and 15% by weight S, no non-condensable products are produced. Such a grain can be formed from a compacted mixture of finely divided aluminum and sulphur or finely divided aluminum can be dispersed in melted sulphur and the material cast to form a grain of suitable configuration. Any hydrogen present reacts to form H 5 and any oxygen present reacts to form S In Example 2, the sulphur was admixed with the aluminum fuel, however, the sulphur could have been just as readily added to the system by injection into the combustion chamber or by admixture with the working fluid at a point downstream of the combustion chamber and upstream of the condensuctor. If the sulphur is not contained within the fuel, it should be added at a point within the system where the temperature is sufiiciently high to allow the sulphur to react with the undesirable products and at a point sufficiently upstream from the condensuctor to allow, considering the reaction kinetics, suflicient dwell time prior to dumping for the reactions to reach equilibrium. 7 7. EXAMPLE 3 A system in which an organic sulphur compound is used is exemplified by one in which the fuel comprises a slurry consisting of 25% dimethylsulfone (C H SO and 75% finely divided magnesium, and the oxidizer is hydrogen peroxide. Under these circumstances, stoichiometric reaction requires that the oxidizer release sufficient oxygen to react with all the magnesium, carbon and hydrogen, but not to react with the sulphur. Based on 100 grams of fuel, the reaction is:

(As in the above examples, sea water could be added to the combustion products to bring the combustion temperature to a manageable value of about 1800 F.) The excess sulphur produced by this combination is sufiicient to react with the hydrogen to form H in the event of a fuel-rich deviation from stoichiometric of up to 8.9%. On the other hand, in case the oxidizer is in excess and O is liberated, the system is capable of reacting with 4.08% excess hydrogen peroxide, in which case S0 would form.

While this invention has been described with respect to certain specific examples, various modifications and substitutions can be made without departing from the scope of this invention. The invention is limited only by the following claims wherein:

Iclairn:

1. A method for generating a working fluid for use in an underwater power plant which working fluid is substantially free of non-condensable gaseous components at a predetermined range of fuel and oxidizer rich nonstoichiometric oxidizer to fuel ratios which comprises reacting in a chamber, a non-nitrogenous fuel material with a non-nitrogenous oxidizer material to generate heat and reaction products and reacting said reaction products with an amount of a material selected from the group consisting of sulphur and non-nitrogenous sulphur compounds sufficient to react with substantially all non-condensable gases present in the gaseous component of said reaction products at the limits of said range of non-stoichiometric oxidizer to fuel ratios.

2. The method of claim 1 wherein said material is reacted with said combustion products by introducing said material into said combustion chamber.

3. The method of claim 2 wherein said material is admixed with said fuel material.

4. The method of claim 1 wherein said fuel comprises a material selected from the group consisting of metals, metal hydrides, metal carbides and metal borides and mixtures thereof.

5. The method of claim 4 wherein the oxidizer comprises a material selected from the group consisting of oxygen, water, hydrogen peroxide, metallic peroxides, non-nitrogenous oxidizing salts, non-nitrogenous oxidizing acids, water-soluble halogens, interhalogen compounds of water-soluble halogens, and mixtures thereof.

6. The method of claim 1 wherein said combustion products are mixed with water to generate a mixture of combustion products and steam.

7. The method of claim 1 further comprising the steps of utilizing the energy of said working fluid and exhausting the spent working fluid into ambient water.

8. A method for generating a gaseous working fluid free of non-condensable gases over a range of fuel and oxidizer rich non-stoichiometric oxidizer to fuel ratios for use in an underwater power plant which comprises reacting, in a chamber, a non-nitrogenous fuel material and a non-nitrogenous oxidizer material to generate hot reaction products, mixing water with said reaction products to form a lower temperature working fluid, and reacting non-condensable gases formed during the produc tion of said reaction products and said working fluid with an amount of a material selected from the group consisting of sulphur and non-nitrogenous sulphur compounds sufiicient to react with substantially all said noncondensable gases present at the limits of said range of nonstoichiometric oxidizer to fuel ratios.

9. The method of claim 8 further comprising the steps of utilizing the energy of said working fluid and exhausting the spent working fluid into ambient water.

10. The method of claim 9 wherein said working fluid comprises less than 5% by volume of CO References Cited UNITED STATES PATENTS 2,744,380 5/1956 McMillan et a1 -207 2,996,877 8/1961 McMillan 60216 X 3,158,993 12/1964 Hodgson 60-216 X 3,158,994 12/1964 Hodgson l49-37 X BENJAMIN R. PADGETT, Primary Examiner. 

